spend a lot of time to fix this error.
hum Blizzard...
Somewhere in the code, the editbox is not anchor anymore to the chatframe, so call GetRight and GetLeft return nil.
Add this code somewhere.
Code:
local tt = ChatEdit_UpdateHeader;
ChatEdit_UpdateHeader = function(editBox)
local header = _G[editBox:GetName().."Header"];
header:ClearAllPoints();
header:SetPoint("LEFT", editBox, "LEFT", 15, 0);
if header:GetRight() ~= nil and header:GetLeft() ~= nil then
tt(editBox);
end
end